The present invention relates to a method of ionising a sample, a method of mass spectrometry, apparatus for ionising a sample and a mass spectrometer.
In targeted analysis using mass spectrometry it is known to run one or more survey or calibration experiments using standard solutions of target analytes with or without a matrix. These survey experiments allow the optimum instrument parameters to be determined for each analyte and also allow the instrument parameters to be associated with the retention time window of each target. The conditions depend on both the target compound and the chromatographic conditions e.g. flow rate, eluent composition and temperature.
It is known to add a reagent to the eluent emerging from a liquid chromatography separator before the eluent passes to an ionisation source and is then ionised and the resulting ions are subsequently mass analysed by a mass analyser. The process of adding a reagent to the eluent emerging from a liquid chromatography separator is commonly referred to as post column addition.
The addition of a reagent downstream of a chromatographic separation (e.g. post column) and upstream of an ionisation source allows the nature of the ions which are subsequently formed by the ionisation source to be altered to optimise the conditions for analysis and detection without compromising the conditions required for separation of analyte molecules as the analyte molecules pass through the upstream chromatographic separation device.
It is known that the addition of a post column reagent may result in modification of endogenous matrix or background ions and/or specific target analytes.
N. Volpi and R. J. Linhardt “High-performance liquid chromatography-mass spectrometry for mapping and sequencing glycosaminoglycan-derived oligosaccharides” Nat Protoc. 2010 June; 5(6), p. 993-1004 discloses post-column addition of tributylamine/acetonitrile which has the advantage of causing the disappearance of certain cation adduct peaks e.g. Na+, K+ or NH4+ which results in mass spectra exhibiting reduced chemical noise thereby producing simplified and more readily interpretable mass spectra.
US 2008/0090298 (Apffel) discloses a method of protein analysis mass spectrometry. In one arrangement, a reagent is added to eluent from a liquid chromatography separation device to cleave crosslinking.
Yun Zhang et al: “Coupling of liquid chromatography with mass spectrometry by desorption electrospray ionisation” Chemical Communications; 1 Jan. 2011; vol. 47 no. 14; p. 4171 and US 2013/023005 (Chen) both disclose a method of desorption electrospray ionisation (DESI) wherein a solvent is added to a chromatographic effluent prior to ionisation in order to enhance ionisation efficiency.
It is desired to provide an improved mass spectrometer.